The present invention relates to fabrication of integrated circuits, and, more particularly, to photochemical patterning of thin films during fabrication of integrated circuits.
Integrated circuits are typically fabricated by many step processes creating patterns of various materials in layers upon a semiconductor or other substrate. The patterned layers are usually formed by first depositing a layer of material over all the the preceding layers, then spinning on a photoresist, projecting light through a photomask with the desired pattern onto the photoresist thereby exposing it with the pattern, developing the photoresist to remove that portion not part of the pattern, and lastly, using the thus patterned photoresist as an etch mask for etching away the exposed portion (i.e., that portion not covered by the patterned photoresist) of the deposited layer of material. Such photoresist aided patterning has problems including particulate contamination and the contamination and cleanup required by use of the wet chemistry and atmospheric pressures involved.
Alternative patterning schemes not relying on photoresist include direct deposit of material only in the pattern regions. An example of such a process is as follows: flow a gas containing a compound of the material to be deposited over the substrate and photochemically decompose the gas to deposit the material at the pattern site by use of a laser. This system appears in Deutsch et al, U.S. Pat. No. 4,340,617 wherein an argon-helium laser is used to decompose trimethylcadmium to deposit cadmium. the problems of such a photochemical system include the poor electrical and mechanical properties of the deposited patterned material films.
Similarly, pyrolytic decomposition of a gas containing a compound of the material-to-be-deposited at pattern sites by locally heating the substrate selectively at pattern sites avoids the use of photoresist. An example of such a system appears in Herman et al., Materials Research Society Symposium Proceedings vol. 17 (1983) wherein a laser is used to provide the local heating and compounds such as nickel tetracarbonyl is decomposed to deposit patterns of nickel. Herman et al. also compare the rates of pyrolytic and photochemical depositions and conclude that the pyrolytic is generally preferable. Further, Herman et al., Material Research Society Conference (Boston, Nov. 15, 1983) report complete fabrication of a MOS transistor by pyrolytic deposition: silane was decomposed to deposit silicon, phosphine decomposed to dope silicon with phosphorous, hydrogen chloride and chlorine decomposed to etch silicon, tungsten hexafluoride decomposed to deposit tungsten, and so forth. However, such photoresist independent deposition and patterning yields layers of material that have poor electrical and mechanical properties.
Thus it is a problem of the known systems of deposition and patterning to provide both good electrical and mechanical properties of the deposited patterns of material and a dry and controlled atmosphere for the process sequence.